1. Field of the Invention
One embodiment of the present invention relates to a display device.
One embodiment of the present invention relates to an object, a method, or a manufacturing method. One embodiment of the present invention relates to a process, a machine, manufacture, or a composition of matter. One embodiment of the present invention relates to a semiconductor device, a light-emitting device, a power storage device, a memory device, a driving method thereof, or a manufacturing method thereof. In particular, one embodiment of the present invention relates to a semiconductor device, a display device, or a light-emitting device each including an oxide semiconductor.
In this specification and the like, a semiconductor device generally means a device that can function by utilizing semiconductor characteristics. A display device, an electro-optical device, a semiconductor circuit, and an electronic device each include a semiconductor device in some cases.
2. Description of the Related Art
Specifically proposed structures of active matrix display devices including light-emitting elements are different depending on manufacturers. However, in general, at least a light-emitting element, a transistor that controls input of a video signal to a pixel (a switching transistor), and a transistor that controls the value of current supplied to the light-emitting element (a driving transistor) are provided in each pixel.
When all the transistors in pixels have the same polarity, it is possible to omit some of steps for manufacturing the transistors, for example, a step of adding an impurity element imparting one conductivity type to a semiconductor film Patent Document 1 discloses a light-emitting element type display in which transistors included in pixels are all n-channel transistors.
In an active matrix display device including light-emitting elements, variation in threshold voltage among transistors that control the values of current supplied to the light-emitting elements in accordance with image signals (driving transistors) is likely to influence the luminance of the light-emitting elements. Patent Document 2 discloses a circuit structure for preventing the variation in threshold voltage among the driving transistors from influencing the luminance of the light-emitting elements.